Mechanical recycling methods for polyolefins

Abstract

A polyolefin mechanical recycling process in which a specific combination of processing steps, in a given sequence, results in a high purity recycled polyolefin grade having a balanced set of mechanical and optical properties that are superior to those typically found in similar recycled polyolefin grades, and a polyolefin mechanical recycling apparatus for carrying out said polyolefin mechanical recycling process.

Description

Technical Field

[0001] The present invention relates to a mechanical recycling method of polyolefin for obtaining a high purity recycled polyolefin grade having balanced mechanical properties and optical properties superior to those usually found in similar recycled polyolefin grades by a specific combination of processing steps in a given order, and a mechanical recycling apparatus for polyolefin for carrying out the mechanical recycling method of the polyolefin.

Background Art

[0002] In the past decade, attention has been increasing on the environmental sustainability of plastics and their current usage. As a result, new laws regarding the disposal, collection, and recycling of polyolefins have been enacted. Furthermore, in many countries, efforts are being made to increase the proportion of plastic materials that are recycled instead of being sent to landfill sites.

[0003] In Europe, plastic waste accounts for approximately 27 million tons of waste per year. In 2016, of this, 7.4 million tons were disposed of in landfill sites, 11.27 million tons were burned (for energy production), and approximately 8.5 million tons were recycled. Polypropylene-based materials are particularly problematic because these materials are widely used in packaging. Considering that the amount of waste collected is huge compared to the amount of waste (only about 30%) that is recycled and returned to the stream, there is still great potential for the intelligent reuse of plastic waste streams and the mechanical recycling of plastic waste.

[0004] Let's take the automotive industry as an example. In Europe, the EU's End-of-Vehicle (ELV) Directive stipulates that 85% / 95% of materials from vehicles must be recyclable or recoverable. Current recycling rates for automotive parts fall far short of this target. On average, vehicles are composed of 9% by weight of plastic, but only 3% of this 9% is currently recycled. Therefore, if the plastic recycling target in the automotive industry is to be achieved, there are still requirements that need to be met. This invention focuses particularly on mechanically recycled waste streams, rather than "energy recycling," which involves burning polyolefins for energy. However, due to cost, low mechanical properties, and poor processing properties, waste streams containing cross-linked polyolefins are often used for energy recovery (e.g., incineration in district heating plants or heat generation in the cement industry) and are rarely recycled into new products.

[0005] One of the main trends in the polyolefin sector is the use of recycled materials from various sources. Durable goods streams, such as those derived from waste electrical equipment (WEE) or end-of-life vehicles (ELV), contain a variety of plastics. These materials can be processed to recover acrylonitrile butadiene styrene (ABS), high-impact polystyrene (HIPS), polypropylene (PP), and polyethylene (PE) plastics. Separation can be performed using density separation in water, and then further separation can be performed based on fluorescence, near-infrared absorption, or Raman fluorescence. However, obtaining pure recycled polypropylene or pure recycled polyethylene is generally very difficult. Generally, commercially available recycled polypropylene is a mixture of both polypropylene (PP) and polyethylene (PE), which is especially true for spent waste streams. Commercially available recyclable materials from spent waste sources generally contain a mixture of PP and PE, with trace components found to be <50% by weight.

[0006] The better the quality of the recycled polyolefin, that is, the higher its purity, the more expensive the material becomes. Furthermore, recycled polyolefin materials are often cross-contaminated with non-polyolefin materials such as polyethylene terephthalate, polyamide, and polystyrene, or with non-polymeric substances such as wood, paper, glass, or aluminum.

[0007] Furthermore, materials containing a large amount of recycled polypropylene, such as polypropylene-rich materials, typically have far worse properties than virgin materials unless the amount of recycled polyolefin added to the final formulation is extremely small. For example, such materials often have a bad odor and taste, low rigidity, low impact strength, and poor mechanical properties (e.g., brittleness), thus failing to meet customer requirements. [Overview of the Initiative] [Means for solving the problem]

[0008] This invention is based on the observation that a specific combination of processing steps in a given order can yield a high-purity recycled polyolefin grade having a better-balanced set of mechanical and optical properties than those typically found in similar recycled polyolefin grades. Furthermore, the specific combination of steps means that the quality of the high-purity recycled polyolefin grade is less dependent on the quality of the raw materials, which are known to vary greatly depending on the source of the raw materials.

[0009] Thus, in the first aspect, the present invention, in a given order, Step a) provides a precursor mixed plastic recycling stream (A), Step b) involves sieving the aforementioned precursor mixed plastic recycling stream (A) to create a sieved mixed plastic recycling stream (B) containing only items with a maximum length in the range of 30 to 400 mm, Step c) wherein the sieved mixed plastic recycling stream (B) is sorted by one or more optical sorters to produce one or more single-color sorted polyolefin recycling streams (C) and mixed color sorted polyolefin recycling streams (CM), wherein the sieved mixed plastic recycling stream (B) is sorted by at least color, and optionally by polyolefin type and / or form of article, and each of the one or more single-color sorted polyolefin recycling streams (C) and the mixed color sorted polyolefin recycling streams (CM) is subjected separately to step d) and subsequent steps, Step d) reducing the size of the selected polyolefin recycling stream (C or CM) pieces to form a flake-like polyolefin recycling stream (D), Step e) involves generating a first suspended polyolefin recycling stream (E) by washing the flake-like polyolefin recycling stream (D) with a first aqueous washing solution (W1) without inputting thermal energy, Step f) removes at least a portion, preferably substantially all, of the first aqueous cleaning solution (W1) from the first suspended polyolefin recycling stream (E) to obtain the first washed polyolefin recycling stream (F), Step g) is to wash the first washed polyolefin recycling stream (F) with a second aqueous washing solution (W2) to produce a second suspended polyolefin recycling stream (G), wherein sufficient thermal energy is introduced into the second suspended polyolefin recycling stream (G) so that the temperature during washing is in the range of 65 to 95°C. Step h) removes the second aqueous cleaning solution (W2) and any materials that do not float on the surface of the second aqueous cleaning solution from the second suspended polyolefin recycling stream (G) to obtain a second cleaned polyolefin recycling stream (H), Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), If necessary, step j) separates the dried polyolefin recycling stream (I) into a light fraction and a heavy fraction of polyolefin recycling stream (J), Step k) involves using one or more optical sorters to sort the one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, and further sorting the dried polyolefin recycling stream (I) in the absence of the heavy fraction polyolefin recycling stream (J) or step j) to obtain a purified polyolefin recycling stream (K), If necessary, step l) melt-extrude the purified polyolefin recycled stream (K), preferably pelletized, to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in a molten state. If necessary, step m) aerate the purified polyolefin recycling stream (K) in the absence of the recycled polyolefin product (L) or step l) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin product (M), which is either an aerated and extruded recycled polyolefin product (M1) or an aerated recycled polyolefin flake (M2). The present invention relates to a mechanical recycling method for polyolefins, wherein the purified polyolefin recycling stream (K), comprising the above, is first aerated to form aerated recycled polyolefin flakes (M2), and then extruded, preferably with the order of steps l) and m) reversed so that the additive (Ad) is added in a molten state, to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3).

[0010] In yet another aspect, the present invention relates to a mechanical recycling apparatus for polyolefins for carrying out the mechanical recycling method for polyolefins described in any one of the prior claims.

[0011] definition Used waste refers to objects that have completed at least their first use cycle (or lifecycle), meaning they have already achieved their initial purpose, while industrial waste typically refers to manufacturing scrap that does not reach consumers.

[0012] A recycling stream may contain both the article to be recycled and fragments (such as flakes) of the article to be recycled. In the context of this invention, the contents of a recycling stream are referred to as pieces, whether they are whole articles, fragments thereof, or flakes thereof. In some embodiments, a piece may be a flake, while in other embodiments, a piece may be a larger object that can be converted into flakes at a later stage.

[0013] In the context of the present invention, a mixed plastics recycling stream may be any recyclable stream in which polyolefins are present and the stream does not consist solely of a single polyolefin product, such as in the case of a post-industrial waste recycling stream in which a single polyolefin grade manufacturing waste or a single polyolefin-containing article may be the only piece present in the stream. Generally speaking, all polyolefin-containing spent waste recycling streams, like many polyolefin-containing post-industrial waste recycling streams, become mixed plastics recycling streams.

[0014] As used herein, the term “form of article” refers to the shape and form of an article present in a polyolefin recycling stream. Such articles may, among other things, be present in the form of films, bags, and pouches, which are considered flexible articles, and may, among other things, be present in the form of molded articles such as food containers, skincare product containers, and plastic bottles, which are considered rigid articles. Commercial optical sorters such as Tomra Autosort, RTT Steinert Unisort, and Redwave Pellenc can separate so-called rigid articles from so-called flexible articles by utilizing aerodynamic properties (i.e., a stream of gas is usually applied to the stream, and articles that are rigid articles fall in a different arc than flexible articles), and can convert a stream containing such articles into a so-called rigid stream and a flexible stream.

[0015] According to the present invention, as a result of a sorting method for sorting polyolefin-containing articles by at least their color, one or more monochromatic sorted polyolefin streams (C) are obtained as an intermediate product. Those skilled in the art will recognize that a significant amount of polyolefin-containing articles in any given mixed-color recycling stream are transparent, i.e., colorless. For the purposes of the present invention, any transparent, i.e., colorless polyolefin-containing articles are considered a separate color classification, and as a result, monochromatic sorted polyolefin streams (C) whose "color" is colorless (i.e., transparent) are obtained. In some embodiments, this colorless polyolefin recycling stream is taken through subsequent steps of the method to obtain a colorless recycling product, or in other embodiments, the colorless polyolefin recycling stream is mixed with a non-colorless monochromatic recycling stream (e.g., a white polyolefin recycling stream), and the mixed stream is considered a non-colorless monochromatic recycling stream (i.e., a mixture of a colorless stream and a white stream is then considered a white stream). While we do not wish to be bound by theory, it is thought that the addition of colorless polyolefins to a non-colorless polyolefin recycling stream does not significantly affect the final color of the recycled product.

[0016] According to the present invention, it is important that both one or more monochromatic sorted recycled streams (C) and mixed-color sorted polyolefin recycled streams (CM) are subjected to subsequent processing steps d) to m). In the context of the present invention, the term “monochromatic” should be interpreted as meaning substantially the same color; that is, a polyolefin stream containing pieces of various shades of red is classified as a monochromatic stream, while a polyolefin stream containing pieces of red and yellow is not classified as a monochromatic stream. The accuracy of monochromatic selection depends on the technique used for sorting by color and is therefore limited by the available techniques. Since the impression of color to the human eye cannot be strictly defined by wavelength, and the same color may be obtained with a single wavelength of light or a combination of different wavelengths, the definition on the CIELAB color scale is the most appropriate descriptor. Particularly preferably, the same color means ΔE < 50, preferably ΔE < 40, more preferably ΔE < 30, and most preferably ΔE < 30. ΔE is defined by the following formula:

number

[0017] Furthermore, those skilled in the art will recognize that in prior art sorting methods that include an automatic sorter of the type discussed below, perfect sorting is not achieved, which means that any phrase such as "the stream contains only a single color" or "the stream contains only a single polyolefin type" is broadly interpreted, and a stream described in this way contains substantially only the described color or polyolefin type, but due to the technical limitations of the sorting step, it will be recognized that it is not 100% pure.

[0018] However, those skilled in the art will recognize that sorting by an optical sorter, i.e., an automatic sorter of the type discussed below, provides a much more accurate sorting than so-called "coarse sorting" where articles are separated by simple visual inspection and assigned to color portions corresponding to their dominant colors. The results of such "coarse sorting" will not constitute a single-color polyolefin stream within the meaning of the present invention.

[0019] Similarly, a mixed-color sorted polyolefin recycle stream (CM) obtained through such a sorting process will necessarily be lacking in one or more colors and thus is not equivalent to a mixed-color polyolefin recycle stream that has not undergone one or more sorting steps.

[0020] Those skilled in the art will recognize that although pH values greater than 14.0 and less than 0.0 are theoretically possible, it is very difficult to measure such pH values using conventional pH probes. Thus, in the context of the present invention, an aqueous solution having an effective pH greater than 14.0 is considered to have a pH of 14.0, and an aqueous solution having an effective pH less than 0.0 is considered to have a pH of 0.0.

[0021] In the context of the present invention, the term “washing” is used to refer to the addition of a solvent, usually water, used to remove foreign matter or residual liquid from the surface of the polyolefin. This can be achieved in a very short time, i.e., less than 5 minutes, often less than 1 minute, in contrast to a “washing” step, which usually requires a longer time and stirring, as it may remove foreign matter adhering to the surface of the polyolefin and potentially extract volatile organic compounds from the polyolefin.

[0022] Where the term “includes” is used in this specification and claims, it does not preclude other unspecified elements having primary or secondary functional importance. For the purposes of the present invention, the term “consisting of” is considered a preferred embodiment of the term “includes.” Hereinafter, where a group is defined to include at least a certain number of elements, this is also understood to disclose a group preferably consisting only of these elements.

[0023] When an indefinite or definite article, such as "a," "an," or "the," is used to refer to a singular noun, it also includes the plural form of that noun unless otherwise specified. [Brief explanation of the drawing]

[0024] [Figure 1] Preferred configuration of the optical sorting machine in step c). [Modes for carrying out the invention]

[0025] The present invention, in a given order, Step a) provides a precursor mixed plastic recycling stream (A), Step b) involves sieving the precursor mixed plastic recycling stream (A) to create a sieved mixed plastic recycling stream (B) containing only items with a maximum length in the range of 30 to 400 mm, Step c) wherein the sieved mixed plastic recycling stream (B) is sorted by one or more optical sorters to produce one or more single-color sorted polyolefin recycling streams (C) and mixed-color sorted polyolefin recycling streams (CM), wherein the sieved mixed plastic recycling stream (B) is sorted by at least color, and optionally by polyolefin type and / or form of article, and each of the one or more single-color sorted polyolefin recycling streams (C) and mixed-color sorted polyolefin recycling streams (CM) is subjected separately to step d) and subsequent steps, Step d) reducing the size of the selected polyolefin recycling stream (C or CM) pieces to form a flake-like polyolefin recycling stream (D), Step e) involves generating a first suspended polyolefin recycling stream (E) by washing the flake-like polyolefin recycling stream (D) with a first aqueous washing solution (W1) without inputting thermal energy, Step f) removes at least a portion, preferably substantially all, of the first aqueous cleaning solution (W1) from the first suspended polyolefin recycling stream (E) to obtain the first washed polyolefin recycling stream (F), Step g) is to wash a first washed polyolefin recycling stream (F) with a second aqueous washing solution (W2) to produce a second suspended polyolefin recycling stream (G), wherein sufficient thermal energy is introduced into the second suspended polyolefin recycling stream (G) so that the temperature during washing is in the range of 65 to 95°C. Step h) removes the second aqueous cleaning solution (W2) and any materials that do not float on the surface of the second aqueous cleaning solution from the second suspended polyolefin recycling stream (G) to obtain the second washed polyolefin recycling stream (H), Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), If necessary, step j) separates the dried polyolefin recycling stream (I) into light and heavy polyolefin recycling streams (J), Step k) involves using one or more optical sorters to separate one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, and further sorting the dry polyolefin recycling stream (I) in the absence of the heavy fraction polyolefin recycling stream (J) or step j) to obtain a purified polyolefin recycling stream (K), If necessary, step l) melt-extrude the purified polyolefin recycled stream (K), preferably pelletized, to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in a molten state. If necessary, step m) aerate (aerate) the purified polyolefin recycling stream (K) in the absence of the recycled polyolefin product (L) or step l) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin product (M), which is either an aerated and extruded recycled polyolefin product (M1) or an aerated recycled polyolefin flake (M2). The present invention relates to a mechanical recycling method for polyolefins, wherein a purified polyolefin recycling stream (K) containing is first aerated to form aerated recycled polyolefin flakes (M2), and then extruded, preferably with the order of steps l) and m) reversed so that an additive (Ad) is added in a molten state, to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3).

[0026] In one embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step k) further sorting the dried polyolefin recycling stream (I) using one or more optical sorters that sort one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, to obtain a purified polyolefin recycling stream (K). Includes.

[0027] In another embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step j) separates the dried polyolefin recycling stream (I) into a light fraction and a heavy fraction of the polyolefin recycling stream (J), Step k) further sorting the heavy fraction polyolefin recycling stream (J) using one or more optical sorters that sort one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, to obtain a purified polyolefin recycling stream (K). Includes.

[0028] In yet another embodiment, steps i) onward are performed in a given order. Step j) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step k) further sorting the dried polyolefin recycling stream (I) using one or more optical sorters that sort one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, to obtain a purified polyolefin recycling stream (K), Step l) wherein a purified polyolefin recycled stream (K) is melt-extruded, preferably pelletized, to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in a molten state. Includes.

[0029] In yet another embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step j) separates the dried polyolefin recycling stream (I) into a light fraction and a heavy fraction of the polyolefin recycling stream (J), Step k) further separating the heavy fraction polyolefin recycling stream (J) using one or more optical sorters that separate one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, in order to obtain a purified polyolefin recycling stream (K), Step l) wherein a purified polyolefin recycled stream (K) is melt-extruded, preferably pelletized, to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in a molten state. Includes.

[0030] In yet another embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step k) further sorting the dried polyolefin recycling stream (I) using one or more optical sorters that sort one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, to obtain a purified polyolefin recycling stream (K), Step m) to produce aerated recycled polyolefin flakes (M2) by aerating the purified polyolefin recycled stream (K) to remove volatile organic compounds. Includes.

[0031] In another embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step j) separates the dried polyolefin recycling stream (I) into a light fraction and a heavy fraction of the polyolefin recycling stream (J), Step k) further separating the heavy fraction polyolefin recycling stream (J) using one or more optical sorters that separate one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, in order to obtain a purified polyolefin recycling stream (K), Step m) to produce aerated recycled polyolefin flakes (M2) by aerating the purified polyolefin recycled stream (K) to remove volatile organic compounds. Includes.

[0032] In yet another embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step k) further sorting the dried polyolefin recycling stream (I) using one or more optical sorters that sort one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, to obtain a purified polyolefin recycling stream (K), Step l) wherein a purified polyolefin recycled stream (K) is melt-extruded, preferably pelletized, to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in a molten state. Step m) to produce an aerated and extruded, preferably pelletized, recycled polyolefin product (M1) by aerating the recycled polyolefin product (L) to remove volatile organic compounds, and Includes.

[0033] In yet another embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step j) separates the dried polyolefin recycling stream (I) into a light fraction and a heavy fraction of the polyolefin recycling stream (J), Step k) further separating the heavy fraction polyolefin recycling stream (J) using one or more optical sorters that separate one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, in order to obtain a purified polyolefin recycling stream (K), Step l) wherein a purified polyolefin recycled stream (K) is melt-extruded, preferably pelletized, to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in a molten state. Step m) to produce an aerated and extruded, preferably pelletized, recycled polyolefin product (M1) by aerating the recycled polyolefin product (L) to remove volatile organic compounds, and Includes.

[0034] In yet another embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step k) further sorting the dried polyolefin recycling stream (I) using one or more optical sorters that sort one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, to obtain a purified polyolefin recycling stream (K), Step m) involves aerating the purified polyolefin recycling stream (K) to remove volatile organic compounds, thereby producing aerated recycled polyolefin flakes (M2), Step l) wherein aerated recycled polyolefin flakes (M2) are melt-extruded, preferably pelletized, to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3), wherein preferably an additive (Ad) is added in a molten state. Includes.

[0035] In the final embodiment, steps i) onward are performed in a given order. Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I), Step j) separates the dried polyolefin recycling stream (I) into a light fraction and a heavy fraction of the polyolefin recycling stream (J), Step k) further separating the heavy fraction polyolefin recycling stream (J) using one or more optical sorters that separate one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, in order to obtain a purified polyolefin recycling stream (K), Step m) involves aerating the purified polyolefin recycling stream (K) to remove volatile organic compounds, thereby producing aerated recycled polyolefin flakes (M2), Step l) wherein aerated recycled polyolefin flakes (M2) are melt-extruded, preferably pelletized, to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3), wherein preferably an additive (Ad) is added in a molten state. Includes.

[0036] While we do not wish to be bound by theory, performing step m) before step l) is advantageous because the improved surface area-to-volume ratio of the polyolefin flakes means that more volatile organic compounds can be removed. However, performing step l) before step m) is considered advantageous because extrusion may generate new volatile organic compounds through the decomposition of the polyolefin or contaminants (e.g., PVC or PET), or it may move volatile organic compounds that are not close to the surface of the flakes to the surface of the extruded product, potentially increasing the odor. Which embodiment is preferred will differ depending on the method and will need to be optimized accordingly.

[0037] Step a) involves providing a precursor mixed plastic recycling stream (A).

[0038] This precursor mixed plastic recycling stream (A) may originate from used waste, post-industrial waste, or a combination thereof.

[0039] Preferably, the precursor mixed plastic recycling stream (A) is derived from used waste.

[0040] As those skilled in the art will recognize, the provision of such a precursor mixed plastic recycling stream may involve the collection of suitable polyolefin-containing materials from post-consumer sources (e.g., roadside recycling bins) or post-industrial sources, or pre-collected mixed plastic recycling streams may be purchased from any number of recycling companies.

[0041] The form of the precursor mixed plastic recycling stream (A) is not important, but it is required that the items present in the precursor mixed plastic recycling stream (A) do not stick together in steps b) to m). The most common form of commercially available mixed plastic recycling stream is in the form of a bale. If the precursor mixed plastic recycling stream (A) is supplied in the form of a bale, the bale must be broken up before the precursor mixed plastic recycling stream (A) undergoes sieving in step b). Depending on the method used to pack the bale, it may also be necessary to remove any wire used to tie the bale (removing the wire from the bale) and / or empty the bale from its container, such as a plastic bag or packaging material (opening the bag / bale).

[0042] Furthermore, it may be necessary to store intermediate products (i.e., intermediate recycling streams) of the mechanical recycling method for polyolefins (such as at least one of one or more monochromatic sorted polyolefin recycling streams (C) or mixed color sorted polyolefin recycling streams (CM)), in which case these intermediate products can be formed into bales. Any bales formed in this manner must be dismantled, preferably using one of the appropriate methods listed above, before the intermediate products proceed to the next step of the method. Similarly, the intermediate products (i.e., intermediate recycling streams) may be stored, for example, in a suitable container without being formed into bales, in which case the intermediate products can be reintroduced to the next step of the process without the need to dismantle them.

[0043] Those skilled in the art will understand that the scope of the present invention includes not only performing each essential step of the mechanical recycling method for polyolefins in a given order, but also removing intermediate products in bale or other form for a certain period of time, and reintroducing the stored intermediate products into the mechanical recycling method for polyolefins at the location from which they were removed.

[0044] Step b) involves sieving the precursor mixed plastic recycling stream (A) to create a sieved mixed plastic recycling stream (B) that contains only items with a maximum length in the range of 30 to 400 mm.

[0045] Those skilled in the art will recognize multiple methods for achieving the sieving in step b), and therefore this sieving step is not particularly limited. However, preferably, the sieving in step b) is achieved by using sieves with diameters of 30 mm and 400 mm to divide the precursor mixed recycling stream into three streams: a small articles stream with a longest dimension of less than 30 mm, an oversized articles stream with a longest dimension of more than 400 mm, and a sieved mixed plastic recycling stream (B). The small and oversized streams may be discarded or transferred for use in other mechanical recycling methods of polyolefins.

[0046] Step c) is a step of producing one or more monocolor sorted polyolefin recycling streams (C) and mixed color sorted polyolefin recycling streams (CM) by sorting the sieved mixed plastic recycling stream (B) with one or more optical sorters, wherein the sieved mixed plastic recycling stream (B) is sorted at least by color and, if necessary, also by polyolefin type and / or form of article.

[0047] In its broadest sense, any optical sorter can be used to achieve the sorting in step c). In the context of the present invention, the term “optical sorter” refers to a sorting unit that uses any form of electromagnetic radiation (visible or invisible) to distinguish pieces of the sieved mixed plastic recycling stream (B).

[0048] Preferably, the optical sorter in step c) performs sorting by a method selected from the group consisting of a camera system (operating in the visible range of the electromagnetic spectrum), visible reflection spectroscopy, near-infrared spectroscopy, mid-infrared spectroscopy, fast laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy.

[0049] Suitable methods for sorting recycling streams by color include camera systems (operating in the visible range of the electromagnetic spectrum) and visible reflectance spectroscopy.

[0050] Suitable methods for sorting recycling streams by polyolefin type include near-infrared spectroscopy, mid-infrared spectroscopy, fast laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. Near-infrared spectroscopy is particularly preferred.

[0051] Suitable methods for sorting recycling streams by type of item include camera systems (operating within the visible range of the electromagnetic spectrum).

[0052] Preferably, the sorting in step c) is carried out by color and type of polyolefin, meaning that each of the one or more single-color sorted polyolefin recycling streams (C) is single-color and all articles contain a single polyolefin.

[0053] In some embodiments, a single sensor type (e.g., a near-infrared sensor or a camera system operating in the visible range of the electromagnetic spectrum) can be used to distinguish multiple characteristics (e.g., color and type of polyolefin, or color and form of article). Furthermore, many near-infrared sensor units may include a visible reflectance unit or be configured to measure both the near-infrared and visible regions of the electromagnetic spectrum, meaning that a single sensor unit may employ multiple detection methods.

[0054] Multiple detection methods and / or multiple sensors can be used to achieve the sorting in step c).

[0055] More preferably, the sorting in step c) is carried out by color, type of polyolefin, and form of article, meaning that each of the one or more single-color sorted polyolefin recycling streams (C) is single-color, all articles contain a single polyolefin, and each stream contains only rigid or flexible articles.

[0056] The method of the present invention is suitable for isolating any desired polyolefin from a polyolefin mixed recycling stream, but the isolation of polyethylene or polypropylene is particularly desirable. This is because these are likely to be the major polyolefin components of any polyolefin mixed recycling stream, and the isolated polyethylene or isolated polypropylene can be fed into a pure recycled polyolefin stream or extruded and pelletized to obtain pellets of the desired polyolefin, i.e., polyethylene or polypropylene.

[0057] Particularly preferred is that the single-color sorted polyolefin recycled stream (C) is either a single-color sorted polyethylene recycled stream or a single-color sorted polypropylene recycled stream.

[0058] In one embodiment, the mixed color-sorted polyolefin recycled stream (CM) obtained in step c) is then subjected to a sorting step, which sorts according to the type of polyolefin, for example, selecting only polyethylene pieces or only polypropylene pieces.

[0059] In one preferred embodiment, the sorting in step c) separates the filtered mixed plastic recycling stream (B) into a first monocolor sorted polyolefin recycling stream (C1) containing at least a first target polyolefin (PO1), a second monocolor sorted polyolefin recycling stream (C2) containing a second target polyolefin (PO2), and a mixed color sorted polyolefin recycling stream (CM), wherein the first target polyolefin (PO1) and the second polyolefin (PO2) differ in at least one characteristic selected from color, polyolefin type and article form, and the first monocolor sorted polyolefin recycling stream (C1), the second monocolor sorted polyolefin recycling stream (C2), and the mixed color sorted polyolefin recycling stream (CM) are individually subjected to steps d) and beyond.

[0060] By targeting multiple polyolefins, fewer polyolefins are sorted into a high-purity, single-color sorted polyolefin recycling stream from the mixed plastic recycling stream, but the mixed-color sorted polyolefin recycling stream also becomes purer as a result. Furthermore, fewer iterations of the sorting process are required per target polyolefin, thus improving process efficiency.

[0061] If the single-color sorted polyolefin recycling stream (C) is a colorless sorted polyolefin recycling stream, this colorless sorted polyolefin recycling stream may be combined with a different single-color sorted polyolefin recycling stream, such as a white sorted polyolefin recycling stream, before being used in step d) and beyond.

[0062] In one particular embodiment, white sorted polyolefin recycled streams and colorless sorted polyolefin recycled streams are obtained from step c), but mixed-color polyolefin recycled streams (CM) contain all other colors.

[0063] In a particularly preferred embodiment, the sorting in step c) is performed Step c1) involves using a first optical sorter to sort the filtered polyolefin recycling stream (B) to obtain a fraction (C4) containing two target polyolefins (PO1 and PO2) and a mixed color recycling stream (C5), Step c2) involves using a second optical sorter to separate the fraction (C4) containing the two target polyolefins to obtain a first target fraction (C6) containing the first target polyolefin (PO1) and a second target fraction (C7) containing the second target polyolefin (PO2), Step c3) further purifies the first target fraction (C6) and the second target fraction (C7) using a third optical sorter to remove any articles that do not contain the first target polyolefin (PO1) from the first target fraction (C6) and any articles that do not contain the second target polyolefin (PO2) from the second target fraction (C7), thereby obtaining a first monochromatic sorted polyolefin recycling stream (C1), a second monochromatic sorted polyolefin recycling stream (C2), and a further mixed-color recycling stream (C8), wherein the first monochromatic sorted polyolefin recycling stream (C1) and the second monochromatic sorted polyolefin recycling stream (C2) are individually subjected to steps d) and beyond, Step c4) involves supplying a mixed-color recycle stream (C5) and a further mixed-color recycle stream (C8) to a fourth optical sorter to remove any articles containing the first target polyolefin (PO1) or the second target polyolefin (PO2), thereby generating a reclaimed fraction (C9) and a mixed-color polyolefin recycle stream (C3), Step c5) in which the regenerated fraction (C9) is returned to the first optical sorter and supplied during step c1) and The mixed-color polyolefin recycling stream (C3) is then subjected to step d) or further iterations of step c) as a mixed-color sorted polyolefin recycling stream (CM), thereby separating the mixed-color polyolefin recycling stream (C3) into a further first monocolor sorted polyolefin recycling stream (C1), a further second monocolor sorted polyolefin recycling stream (C2), and a further mixed-color polyolefin recycling stream (C3).

[0064] This embodiment will be better understood by referring to Figure 1.

[0065] The labels in Figure 1 correspond to the labels in the embodiments described above, with each solid arrow indicating a recyclable stream en route to one of one or more single-color sorted polyolefin recyclable streams (C), and dashed streams indicating a stream en route to a mixed-color sorted polyolefin recyclable stream (CM).

[0066] It is preferable that the first target polyolefin (PO1) and the second target polyolefin (PO2) are the same color but contain different types of polyolefins, or that the first target polyolefin (PO1) and the second target polyolefin (PO2) contain the same type of polyolefin but have different colors.

[0067] In one particularly preferred embodiment, the first target polyolefin (PO1) is polypropylene having a first desired color and the second target polyolefin (PO2) is polypropylene having a second desired color different from the first desired color, or the first target polyolefin (PO1) is polyethylene having a first desired color and the second target polyolefin (PO2) is polyethylene having a second desired color different from the first desired color.

[0068] It is particularly preferable that the first target polyolefin (PO1) and the second target polyolefin (PO2) are the same color but contain different types of polyolefins.

[0069] In another particularly preferred embodiment, the first target polyolefin (PO1) is polypropylene having a desired color, and the second target polyolefin (PO2) is polyethylene having the same desired color as the first target polyolefin (PO1).

[0070] Alternatively, the first target polyolefin (PO1) and the second target polyolefin (PO2) may be the same color and contain the same type of polyolefin, but have different forms; that is, if the first target polyolefin (PO1) is a rigid white polyethylene recycled stream, then the second target polyolefin (PO2) may be a flexible white polyethylene recycled stream.

[0071] In a particularly preferred embodiment, the sorting in step c) first sorts the sieved mixed plastic recycling stream (B) by type of polyolefin using one or more optical sorters to produce a mixed-color single polyolefin recycling stream (CS), which is then sorted by color to produce one or more single-color sorted polyolefin recycling streams (C) and mixed-color sorted polyolefin recycling streams (CM), each of which contains the same polyolefin, preferably selected from polyethylene and polypropylene.

[0072] By first sorting by type of polyolefin and then by color, it is ensured that the resulting mixed color-sorted polyolefin recycled stream (CM) contains substantially only one type of polyolefin, thereby avoiding the need for further sorting steps in subsequent stages, such as the subsequent sorting steps described above.

[0073] Each of the preferred embodiments described above and below can be combined with the embodiment in which the polyolefin type sorting step precedes the color sorting step, with necessary modifications.

[0074] For example, step c) may first produce a mixed-color single polyolefin recycling stream (CS) by separating the sieved mixed plastic recycling stream (B) by polyolefin type using one or more optical sorters, and this mixed-color single polyolefin recycling stream (CS) is then separated through steps c1) to c5) above, wherein the first target polyolefin (PO1), the second target polyolefin (PO2), and the mixed-color polyolefin recycling stream (C3) are the same type of polyolefin preferably selected from polyethylene and polypropylene.

[0075] The mixed color-sorted polyolefin recycled stream (CM) is particularly preferably a single polyolefin type, more preferably selected from polyethylene and polypropylene. This may be achieved by the embodiment of step c), which includes an initial polyolefin sorting step before the color sorting step, or by sorting the mixed color-sorted polyolefin recycled stream (CM) after the completion of all color sorting steps. Preferably, this is achieved by the embodiment of step c), which includes an initial polyolefin sorting step before the color sorting step.

[0076] The sorting in step c) can be achieved through a simple sorting algorithm in which an optical sensor is programmed to evaluate which pieces should be selected or rejected based on a simple binary decision. Alternatively, a more complex AI-based system can be used to achieve more accurate sorting, especially when sorting by the shape of the items.

[0077] While we do not wish to be bound by theory, the inventors believe that providing a monochromatic sorted polyolefin recycling stream in step c) is essential to obtaining a recycled product with improved properties. As expected, not only is an improvement in the color of the recycled product achieved, but the presence of the important sorting step c) before any of the processing steps d) to m) makes it possible to obtain a purer recycled product. For example, in the sorting by color in step c), only white polyolefin pieces may be selected, and all other colors, including colorless pieces, are removed at this stage. Transparent pieces often originate from plastic bottles, which are often made of PET. Therefore, it is expected that the combined transparent pieces will have a higher PET content than other colors, such as white pieces. PET is easily decomposed during high-temperature washing in step g), for example, and produces small organic molecules, particularly acetaldehyde. Such small organic molecules consequently negatively affect the odor of the recycled product. This problem can be mitigated by reducing the PET content through color sorting at this stage.

[0078] Furthermore, different countries or regions may have different typical colors for different packages, meaning that, for example, green pieces are more likely to contain certain non-polyolefins or undesired polyolefins. The advantages of color sorting in step c) vary depending on which country or region the precursor mixed plastic recycling stream is supplied from.

[0079] In addition, certain colored polymers contain specific pigments / dyes, which can individually lead to contamination of recycled polyolefin products, such as when they contain metallic pigments, are prone to decomposition during extrusion and thus form malodorous compounds, or catalyze the decomposition of polyolefins during extrusion. Removing colored polymers known to contain these pigments / dyes would avoid these problems and lead to improved quality of recycled products.

[0080] Removing specific problematic monochromatic polyolefin recycling streams from mixed color-sorted polyolefin recycling streams (CMs) helps produce high-quality products with a gray / black color (for the same reasons given above for monochromatic recycling products). In this regard, the removal of specific colors can improve the purity of the final gray / black recycling product not only in terms of color, but also in terms of polyolefin content.

[0081] Non-polyolefin and undesired polyolefin flakes can be removed in step k), but any sorting method has limited efficiency, meaning that the higher the purity of the flakes fed into such a method, the higher the purity of the product obtained by such a method. Given the difficulty in obtaining a pure product by conventional methods, even a seemingly small improvement in the purity of the recycled product can be commercially very valuable.

[0082] Furthermore, even if such flakes are removed after washing steps e) and g), the problem of cross-contamination between flakes during steps d) to j) is not avoided.

[0083] Furthermore, the presence of sorting step c) prior to the mechanical recycling steps d) to m) means that the mechanical recycling method for polyolefins according to the present invention allows operators to obtain high-quality recycled products regardless of the quality of the raw materials. The quality of the raw materials can vary greatly in terms of polyolefin content and foreign matter contamination and is well known to depend heavily on the source of the raw materials (i.e., the source of the precursor mixed plastic recycling stream (A)).

[0084] Step d) involves reducing the size of the pieces of the monochromatic sorted polyolefin recycling stream (C or CM) to form a flake polyolefin recycling stream (D).

[0085] The size reduction in step d) may be carried out by any method known to those skilled in the art. One suitable method involves a step of crushing the sorted polyolefin recycled stream (C or CM). Another method involves a step of shredding the sorted polyolefin recycled stream (C or CM). Particularly preferred is that the size reduction in step d) is a shredding step.

[0086] The shredding in step d) may be a wet shredding process or a dry shredding process. Preferably, the shredding in step d) is a wet shredding process in which the sorted polyolefin recycled stream (C or CM) is first brought into contact with an aqueous solution (W0) to provide a sorted suspended polyolefin recycled stream before shredding.

[0087] The selection of the aqueous solution (W0) is not particularly limited, but the pH of the aqueous solution (W0) is preferably in the range of 8.0 to 14.0, more preferably in the range of 10.0 to 14.0, and most preferably in the range of 12.0 to 14.0.

[0088] More preferably, the aqueous solution (W0) is at least a portion of the recycled aqueous cleaning solution removed in step h).

[0089] If the shredding in step d) is a wet shredding process, the resulting flaky polyolefin recycling stream (D) is preferably mechanically dried before step e) begins. Suitable forms of mechanical drying include centrifugal drying and dehydration presses (filters or screw presses), both of which can separate the liquid from the solid.

[0090] Recycling the aqueous cleaning solution used in step h) improves the economics of the method, requiring only one aqueous cleaning solution for use throughout the entire method. Furthermore, the aqueous cleaning solution used in step h) is, by its nature, an alkaline solution, which helps in the removal of impurities in either step d) or step e). It is important to use the cleanest cleaning solution (i.e., the one with the fewest impurities) in the final cleaning step so that the resulting washed polyolefin stream is as clean as possible. Finally, reusing a single aqueous cleaning solution multiple times simplifies the processing of waste streams and avoids the need to process multiple different waste streams containing different chemicals.

[0091] Step e) involves generating a first suspended polyolefin recycling stream (E) by washing the flake polyolefin recycling stream (D) with a first aqueous washing solution (W1) without inputting thermal energy.

[0092] Those skilled in the art will recognize that cleaning steps known in the art may be performed by heating to achieve high-temperature cleaning, or by performing them under ambient conditions to achieve low-temperature cleaning. In this method, step e) corresponds to such low-temperature cleaning.

[0093] Those skilled in the art will recognize that, depending on the selection of the first aqueous cleaning solution (W1), the temperature in step d) may or may not actually match the ambient temperature, for example, because the first aqueous cleaning solution (W1) may become hotter than the ambient temperature due to its use in a previous high-temperature cleaning. Even if the temperature of the first aqueous cleaning solution (W1) is higher than the ambient temperature, it is expected to be considerably lower than the temperature normally required for high-temperature cleaning. Crucial to the definition of step e) is that no further thermal energy is consumed to raise the temperature of the first aqueous cleaning solution (W1) during the cleaning in step e).

[0094] However, the temperature of the first aqueous cleaning solution (W1) in step e) is preferably less than 70°C, more preferably less than 65°C, and most preferably less than 60°C.

[0095] The selection of the first aqueous cleaning solution (W1) is not particularly limited, but the pH of the first aqueous cleaning solution (W1) is preferably in the range of 8.0 to 14.0, more preferably in the range of 10.0 to 14.0, and most preferably in the range of 12.0 to 14.0.

[0096] The first aqueous cleaning solution (W1) may contain detergent in an amount ranging from 0.1% to 1.0% by weight relative to the total weight of the first aqueous cleaning solution (W1).

[0097] The detergent may be a commercially available detergent mixture or may be composed in any way known to those skilled in the art. Suitable detergents include TUBIWASH SKP, TUBIWASH GFN, TUBIWASH EYE, and TUBIWASH TOP, all commercially available from CHT; KRONES colclean AD 1004, KRONES colclean AD 1002, and KRONES colclean AD 1008, all commercially available from KIC KRONES; and P3-stabilon WT and P3 stabilon AL, all commercially available from ECOLAB Ltd.

[0098] More preferably, the first aqueous cleaning solution (W1) is at least a portion of the recycled aqueous cleaning solution removed in step h).

[0099] The advantages of reusing the recycled aqueous cleaning solution from step h) as the first aqueous cleaning solution are the same as the advantages described above with respect to the aqueous solution (W0).

[0100] The washing in step e) is a washing step in contrast to the rinsing step as defined herein, and therefore typically lasts for five minutes or more, for example, from five minutes to four hours.

[0101] The washing in step e) preferably lasts for 5 minutes to 2 hours, more preferably 5 minutes to 1 hour, and most preferably 5 minutes to 30 minutes.

[0102] More preferably, the combination of the first aqueous cleaning solution (W1) and the flake polyolefin recycling stream (D) in step g) is stirred by mechanical mixing, sonication, mechanical grinding, or pump-around loop, and preferably, the combination of the first aqueous cleaning solution (W1) and the flake polyolefin recycling stream (D) in step g) is stirred by sonication. This stirring exposes the flakes in the recycling stream to fresh cleaning solution, so that the process is not hindered by the accumulation of contaminants in the immediate vicinity of the flakes.

[0103] Those skilled in the art will recognize that by combining the various individual methods described above, for example, stirring can be improved by combining mechanical mixing and ultrasonic treatment.

[0104] Step f) involves removing at least a portion, preferably substantially all, of the first aqueous cleaning solution (W1) from the first suspended polyolefin recycling stream (E) to obtain the first washed polyolefin recycling stream (F).

[0105] Those skilled in the art will know that small amounts of foreign matter suspended or dissolved in the first suspended polyolefin recycling stream (E) are removed by the first aqueous washing solution (W1), but step f) does not include targeted removal of foreign matter by, for example, so-called flotation separation, in which case (density 1.00 g / cm³) 3 (Considering that polyolefins of less than a certain amount are expected to float), it will be understood that any foreign matter that does not float on the surface of the solution will be removed by the solution.

[0106] After removing at least a portion of the first aqueous cleaning solution (W1), the first cleaned polyolefin recycling stream (F) may be rinsed with water as needed to remove any remaining traces of the first aqueous cleaning solution (W1) on the surface of the flakes in the first cleaned polyolefin recycling stream.

[0107] Whether or not rinsing is performed, the first washed polyolefin recycling stream (F) may be dried before step g), but it is preferable not to dry the first washed polyolefin recycling stream (F) before step g), because this drying contributes to a decrease in method efficiency from the viewpoint of energy efficiency and step efficiency, but does not significantly contribute to the effects of the present invention.

[0108] Step g) is a step of washing a first washed polyolefin recycling stream (F) with a second aqueous washing solution (W2) to produce a second suspended polyolefin recycling stream (G), wherein sufficient thermal energy is introduced into the second suspended polyolefin recycling stream (G) such that the washing temperature is in the range of 65 to 95°C.

[0109] As mentioned above, those skilled in the art will recognize that cleaning steps known in the art may be performed by heating to achieve high-temperature cleaning, or by performing them under ambient conditions to achieve low-temperature cleaning. The cleaning in step g) is a high-temperature cleaning, in contrast to the cleaning in step e), and thermal energy is introduced so that the temperature during cleaning is 65-95°C.

[0110] The temperature in step g) is in the range of 65 to 95°C, more preferably in the range of 70 to 95°C, and most preferably in the range of 75 to 95°C.

[0111] Preferably, the second aqueous cleaning solution (W2) is an alkaline aqueous cleaning solution.

[0112] Preferably, the pH of the alkaline aqueous cleaning solution is in the range of 9.0 to 14.0, more preferably in the range of 11.0 to 14.0, and most preferably in the range of 12.0 to 14.0.

[0113] Preferably, the alkaline aqueous cleaning solution is an aqueous solution of a base selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide, and mixtures thereof. Most preferably, the second aqueous cleaning solution (W2) is an aqueous solution of sodium hydroxide.

[0114] The amount of base in the alkaline aqueous solution is preferably in the range of 0.05 to 10% by weight, more preferably in the range of 0.10 to 7% by weight, and most preferably in the range of 0.50 to 5% by weight, relative to the total weight of the alkaline aqueous solution.

[0115] In one particularly preferred embodiment, the second aqueous cleaning solution (W2) is a sodium hydroxide solution having a sodium hydroxide concentration in the range of 0.50 to 5.0% by weight relative to the total weight of the second aqueous cleaning solution (W2).

[0116] The second aqueous cleaning solution (W2) may also contain detergent in an amount ranging from 0.1% to 1.0% by weight relative to the total weight of the second aqueous cleaning solution (W2).

[0117] The detergent may be a commercially available detergent mixture or may be composed in any way known to those skilled in the art. Suitable detergents include TUBIWASH SKP, TUBIWASH GFN, TUBIWASH EYE, and TUBIWASH TOP, all commercially available from CHT; KRONES colclean AD 1004, KRONES colclean AD 1002, and KRONES colclean AD 1008, all commercially available from KIC KRONES; and P3-stabilon WT and P3 stabilon AL, all commercially available from ECOLAB Ltd.

[0118] The washing in step g) is a washing step in contrast to the rinsing step as defined herein, and therefore typically lasts for five minutes or more, for example, from five minutes to four hours.

[0119] The washing in step g) preferably lasts for 5 minutes to 2 hours, more preferably 5 minutes to 1 hour, and most preferably 10 minutes to 45 minutes.

[0120] More preferably, the combination of the second aqueous cleaning solution (W2) and the first washed polyolefin recycling stream (F) in step g) is stirred by mechanical mixing, sonication, mechanical grinding, or a pump-around loop, and preferably, the combination of the second aqueous cleaning solution (W2) and the first washed polyolefin recycling stream (F) in step g) is stirred by sonication. This stirring exposes the flakes in the recycling stream to fresh cleaning solution, so that the process is not hindered by the accumulation of contaminants in the immediate vicinity of the flakes.

[0121] Those skilled in the art will recognize that by combining the various individual methods described above, for example, stirring can be improved by combining mechanical mixing and ultrasonic treatment.

[0122] Step h) involves removing the second aqueous cleaning solution (W2) and any materials that do not float on the surface of the second aqueous cleaning solution from the second suspended polyolefin recycling stream (G) to obtain a second cleaned polyolefin recycling stream (H).

[0123] In contrast to step f), in which only a very small amount of foreign matter suspended or dissolved in the washing solution is removed, step h) involves so-called buoyancy separation, which removes any substances that are not suspended on the surface of the washing solution. As those skilled in the art will know, this is 1.00 g / cm³. 3 It will be understood that this has the effect of removing any foreign matter having a density exceeding a certain level.

[0124] While we do not wish to be bound by theory, including a buoyancy separation step immediately after the high-temperature washing in step g) is considered highly beneficial in removing as much foreign matter as possible. Foreign matter removed from the polyolefin flakes may reattach to the polyolefin flakes during subsequent steps of the method, such as aeration (step m) or drying (step i). This can lead to, for example, labeling material adhering to any polyolefin flakes, and if these polyolefin flakes are removed in subsequent steps, such as separation in step j) or sorting in step k), the final recycled product may be contaminated or the yield reduced. Therefore, it is important to perform this step immediately after step g).

[0125] Particularly preferably, the aqueous cleaning solution removed in step h) is recycled for use as the first aqueous cleaning solution (W1) and, if present, as an aqueous solution (W0), as described above.

[0126] If the aqueous cleaning solution removed in step h) is recycled as described above, preferably the foreign matter removed by flotation separation is filtered out of the solution before being used as the first aqueous cleaning solution (W1) and / or aqueous solution (W0).

[0127] After removing the second aqueous cleaning solution (W2), the second washed polyolefin recycling stream (H) may be rinsed with water as needed to remove any remaining traces of the second aqueous cleaning solution (W2) on the surface of the flakes in the second washed polyolefin recycling stream.

[0128] Step i) involves drying the second washed polyolefin recycling stream (H) to obtain a dried polyolefin recycling stream (I).

[0129] The drying in step i) can be achieved by thermal drying, or by a combination of mechanical drying and thermal drying. Suitable forms of mechanical drying include centrifugal drying and dewatering presses (filters or screw presses), both of which can separate the solid from the liquid.

[0130] Step j) involves separating the dried polyolefin recycling stream (I), if present, into light and heavy polyolefin recycling streams (J).

[0131] The light fraction typically contains labels and other non-polyolefin materials, while polyolefin flakes are separated into the heavy fraction's polyolefin recycling stream (J).

[0132] The separation in step j) can be carried out by any known dry density separation technique known in the art. Suitable techniques include airflow classification, wind screens, zigzag cascades, or air separation.

[0133] As those skilled in the art will understand, the separation of light and heavy fractions by such a method is affected not only by the density of the flakes but, more importantly, by the aerodynamic properties of the flakes (typically, by the ratio of surface area to weight). Thus, flat labels are separated from the bulkier polyolefin flakes. The terms “light fraction” and “heavy fraction” are commonly used in the art and do not strictly refer to a classification by density. The meaning of these terms in this invention is consistent with the commonly understood terms in the art.

[0134] Between step j) and step k), there may be an additional step to remove any pieces (so-called splinters) whose longest dimension is less than 2 mm. Any method known to those skilled in the art, such as using a screen or sieve, may be used.

[0135] Step k) involves further separating the heavy fraction polyolefin recycling stream (J) or the dry polyolefin recycling stream (I) in the absence of step j) using one or more optical sorters that sort one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, in order to obtain a purified polyolefin recycling stream (K).

[0136] In step k), at least a first optical separator is used to remove flakes containing one or more materials other than the target polyolefin. The selection criterion for this optical separator is that, if any materials other than the target polyolefin are present in a given flake, these flakes are separated from the stream, and a purified polyolefin recycling stream is obtained.

[0137] When one or more optical sorters sort two or more target polyolefins, the resulting purified polyolefin recycling stream (K) may be a purified mixed polyolefin recycling stream, but preferably, these target polyolefins are separated into separate purified polyolefin recycling streams (K), each containing only a single target polyolefin.

[0138] Multiple optical sorters having the same sorting criteria may be arranged in series to improve the purity of the purified polyolefin recycled stream (K). Alternatively or additionally, multiple optical sorters may be arranged in series to sort according to different criteria, such as color and / or form of the article, but preferably, each of the one or more optical sorters in step k) sorts according to the type of polyolefin as described above.

[0139] Any material removed by one or more optical separators from the heavy fraction polyolefin recycling stream (J), or the dry polyolefin recycling stream (I) in the absence of step j), may be discarded, or returned to the step prior to the mechanical recycling method, either directly or after further separation by optical separators to extract waste flakes containing one or more target polyolefins.

[0140] Step l) involves, if present, melt-extruding a purified polyolefin recycled stream (K), preferably pelletized, to form an extruded, preferably pelletized, recycled polyolefin product (L), preferably involving the addition of an additive (Ad) in a molten state.

[0141] The extrusion of the recycled polyolefin product (L) in step l) is preferably carried out using an extruder, more preferably a uniscrew extruder.

[0142] In particular, it is preferable to use conventional compounding or mixing equipment, such as a single-screw extruder, a conical co-rotating twin-screw extruder, or a plurality of extruders arranged in series (single-screw, twin-screw, or a combination thereof). The recycled polyolefin product (L) recovered from the extruder is usually in the form of pellets, but if step m) is not present in the mechanical recycling method, the recycled polyolefin product (L) may be in the form of an extruded product such as a pipe. Preferably, the recycled polyolefin product (L) is in the form of pellets.

[0143] The optional additive (Ad) added in step l) is selected from additives known in the art, preferably from the group consisting of antioxidants, stabilizers, fillers, colorants, nucleating agents, antistatic agents, and mixtures thereof.

[0144] Such additives are generally available commercially and are described, for example, in Hans Zweifel's "Plastic Additives Handbook," 5th edition, pages 871-873, 2001.

[0145] Step m) involves aerating the recycled polyolefin product (M), which is either an aerated and extruded recycled polyolefin product (M1), preferably a pelletized recycled polyolefin product (M1), or an aerated recycled polyolefin flake (M2), by removing volatile organic compounds from the recycled polyolefin product (L), if present, or the purified polyolefin recycling stream (K), if step l) is not present.

[0146] Aeration in step m) may be achieved, in particular, by the use of air, an inert gas, or steam.

[0147] Preferably, the aeration in step m) is achieved by contacting the recycled polyolefin product (L), or the purified polyolefin recycled stream (K) in the absence of step l), with a gas that is at least 60 volume% N2 gas.

[0148] The temperature at which aeration is performed in step m) may be selected depending on the properties of the polyolefins present in the recycled polyolefin product (L) or the purified polyolefin recycling stream (K).

[0149] The preferred range for general polyolefins is as follows: For HDPE, the preferred temperature range is 50 to 130°C, more preferably 90 to 122°C, and most preferably 100 to 115°C. In the case of LDPE, the temperature range is preferably 50 to 155°C, and more preferably 75 to 105°C. In the case of polypropylene, the temperature range is preferably 50 to 155°C, and more preferably 100 to 150°C.

[0150] It may also be beneficial to perform aeration in step m) under a reduced pressure, for example, less than 500 mbar, more preferably less than 200 mbar, and most preferably less than 100 mbar.

[0151] Aeration in step m) minimizes the content of volatile organic compounds in the aerated recycled polyolefin product (M), thus avoiding the unpleasant odor typically associated with similar recycled polyolefin mixtures. These volatile organic compounds usually originate from contamination of the polyolefin when the consumer first uses it, for example, through contact with food, skincare products, or other toiletry products, or simply from the decomposition of the polyolefin into volatile oligomeric chains during the processing step.

[0152] Device In another aspect, the present invention relates to a mechanical recycling apparatus for polyolefins for carrying out the mechanical recycling method for polyolefins described above.

[0153] All preferred embodiments and alternatives of the above-described mechanical recycling methods for polyolefins are applicable to the mechanical recycling apparatus of the present invention with necessary modifications.

Claims

1. In a given order, Step a) provides a precursor mixed plastic recycling stream (A), Step b) involves sieving the aforementioned precursor mixed plastic recycling stream (A) to create a sieved mixed plastic recycling stream (B) containing only items with a maximum length in the range of 30 to 400 mm, Step c) wherein the sieved mixed plastic recycling stream (B) is sorted by one or more optical sorters to produce one or more single-color sorted polyolefin recycling streams (C) and mixed color sorted polyolefin recycling streams (CM), wherein the sieved mixed plastic recycling stream (B) is sorted by at least color, and optionally by polyolefin type and / or form of article, and each of the one or more single-color sorted polyolefin recycling streams (C) and the mixed color sorted polyolefin recycling streams (CM) is subjected separately to step d) and subsequent steps, Step d) shredding the selected polyolefin recycling stream (C or CM) to form a flake-type polyolefin recycling stream (D), Step e) generating a first suspended polyolefin recycling stream (E) by washing the flake-like polyolefin recycling stream (D) with a first aqueous washing solution (W1) without inputting thermal energy, Step f) removes at least a portion of the first aqueous cleaning solution (W1) from the first suspended polyolefin recycling stream (E) to obtain the first washed polyolefin recycling stream (F), Step g) is to wash the first washed polyolefin recycling stream (F) with a second aqueous washing solution (W2) to produce a second suspended polyolefin recycling stream (G), wherein sufficient thermal energy is introduced into the second suspended polyolefin recycling stream (G) so that the temperature during washing is in the range of 65 to 95°C, Step h) removes the second aqueous cleaning solution (W2) and any materials that do not float on the surface of the second aqueous cleaning solution from the second suspended polyolefin recycling stream (G) to obtain a second cleaned polyolefin recycling stream (H), Step i) to obtain a dried polyolefin recycling stream (I) by drying the second washed polyolefin recycling stream (H), If necessary, step j) separates the dried polyolefin recycling stream (I) into a light fraction and a heavy fraction of polyolefin recycling stream (J), Step k) involves using one or more optical sorters to sort the one or more target polyolefins by removing any flakes containing one or more materials other than the target polyolefin, and further sorting the dried polyolefin recycling stream (I) in the absence of the heavy fraction polyolefin recycling stream (J) or step j) to obtain a purified polyolefin recycling stream (K), If necessary, step l) melt-extrude the purified polyolefin recycled stream (K) to form an extruded recycled polyolefin product (L), If necessary, step m) aerate the purified polyolefin recycling stream (K) in the absence of the recycled polyolefin product (L) or step l) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin product (M), which is either an aerated and extruded recycled polyolefin product (M1) or an aerated recycled polyolefin flake (M2). Includes, A mechanical recycling method for polyolefins, wherein the order of steps l) and m) can be reversed, in which case the purified polyolefin recycling stream (K) is first aerated and then extruded to form aerated recycled polyolefin flakes (M2) that form an extruded aerated recycled polyolefin product (M3).

2. The method according to claim 1, wherein the optical sorter in step c) performs sorting by a method selected from the group consisting of a camera system (operating in the visible range of the electromagnetic spectrum), visible reflection spectroscopy, near-infrared spectroscopy, mid-infrared spectroscopy, fast laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy.

3. The method for mechanically recycling polyolefins according to claim 1, wherein the shredding in step d) is a wet shredding process in which the sorted polyolefin recycling stream (C) is first brought into contact with an aqueous solution (W0) to provide a sorted suspended polyolefin recycling stream before being shredded.

4. The mechanical recycling method for polyolefins according to claim 1, wherein the second aqueous cleaning solution (W2) is an alkaline aqueous cleaning solution.

5. The mechanical recycling method for polyolefins according to claim 1, wherein the second aqueous cleaning solution (W2) is an aqueous solution of a base selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide and mixtures thereof.

6. The mechanical recycling method for polyolefins according to claim 4, wherein the pH of the alkaline aqueous cleaning solution is in the range of 9.0 to 14.

0.

7. The mechanical recycling method for polyolefins according to claim 4, wherein the amount of base in the alkaline aqueous cleaning solution is in the range of 0.05 to 10% by weight of the total weight of the alkaline aqueous cleaning solution.

8. The mechanical recycling method for polyolefins according to any one of claims 1 to 2, 4 to 7, wherein at least a portion of the aqueous cleaning solution (W2) removed in step h) is recycled for use as the first aqueous cleaning solution (W1).

9. The mechanical recycling method for polyolefins according to claim 3, wherein at least a portion of the aqueous cleaning solution (W2) removed in step h) is recycled for use as the first aqueous cleaning solution (W1) and / or the aqueous solution (W0).

10. The mechanical recycling method for polyolefins according to any one of claims 1 to 7, wherein the first aqueous cleaning solution (W1) has a pH in the range of 8.0 to 14.

0.

11. The mechanical recycling method for polyolefins according to claim 3 or claim 9, wherein the aqueous solution (W0) has a pH in the range of 8.0 to 14.

0.

12. The method according to any one of claims 1 to 7, wherein the precursor mixed plastic recycling stream (A) is derived from used waste, post-industrial waste, or a combination thereof.

13. The method according to any one of claims 1 to 7, wherein one of the one or more single-color sorted polyolefin recycled streams (C1) is either a single-color sorted polyethylene recycled stream or a single-color sorted polypropylene recycled stream.

14. The method according to any one of claims 1 to 7, wherein the sorting in step c) sorts the filtered mixed plastic recycling stream (B) into a first monocolor sorted polyolefin recycling stream (C1) containing at least a first target polyolefin (PO1), a second monocolor sorted polyolefin recycling stream (C2) containing a second target polyolefin (PO2), and a mixed color sorted polyolefin recycling stream (CM), wherein the first target polyolefin (PO1) and the second target polyolefin (PO2) differ in at least one characteristic selected from color, polyolefin type and article form, and the first monocolor sorted polyolefin recycling stream (C1), the second monocolor sorted polyolefin recycling stream (C2), and the mixed color sorted polyolefin recycling stream (CM) are each subjected to step d) and subsequent steps.

15. The sorting in step c) is Step c1) involves using a first optical sorter to sort the filtered polyolefin recycling stream (B) to obtain a fraction (C4) containing two target polyolefins (PO1 and PO2) and a mixed color recycling stream (C5), Step c2) is to use a second optical sorter to sort the fraction (C4) containing the two target polyolefins to obtain a first target fraction (C6) containing the first target polyolefin (PO1) and a second target fraction (C7) containing the second target polyolefin (PO2), Step c3), wherein the first target fraction (C6) and the second target fraction (C7) are further purified using a third optical sorter to remove any articles that do not contain the first target polyolefin (PO1) from the first target fraction (C6) and any articles that do not contain the second target polyolefin (PO2) from the second target fraction (C7), thereby obtaining a first monocolor sorted polyolefin recycling stream (C1), a second monocolor sorted polyolefin recycling stream (C2), and a further mixed-color recycling stream (C8), wherein the first monocolor sorted polyolefin recycling stream (C1) and the second monocolor sorted polyolefin recycling stream (C2) are individually subjected to steps d) and beyond, Step c4) involves supplying a mixed-color recycle stream (C5) and a further mixed-color recycle stream (C8) to a fourth optical sorter to remove any articles containing the first target polyolefin (PO1) or the second target polyolefin (PO2) to generate a recycled fraction (C9) and a mixed-color polyolefin recycle stream (C3), Step c5) involves returning the regenerated fraction (C9) to the first optical sorter and supplying it during step c1). The mechanical recycling method for polyolefins according to claim 14, comprising, wherein the mixed-color polyolefin recycling stream (C3) is subjected to step d) and beyond as the mixed-color sorted polyolefin recycling stream (CM) or to further iterations of step c), thereby separating the mixed-color polyolefin recycling stream (C3) into a further first monocolor sorted polyolefin recycling stream (C1), a further second monocolor sorted polyolefin recycling stream (C2), and a further mixed-color polyolefin recycling stream (C3).

16. The mechanical recycling method for polyolefins according to claim 14, wherein the first target polyolefin (PO1) and the second target polyolefin (PO2) are the same color but contain different types of polyolefins, or the first target polyolefin (PO1) and the second target polyolefin (PO2) contain the same type of polyolefin but have different colors.

17. The mechanical recycling method for polyolefins according to claim 16, wherein the first target polyolefin (PO1) is polypropylene having a first desired color, and the second target polyolefin (PO2) is polypropylene having a second desired color different from the first desired color, or the first target polyolefin (PO1) is polyethylene having a first desired color, and the second target polyolefin (PO2) is polyethylene having a second desired color different from the first desired color.

18. The sorting in step c) first sorts the sieved mixed plastic recycling stream (B) according to the type of polyolefin to produce a mixed-color single polyolefin recycling stream (CS), and this mixed-color single polyolefin recycling stream (CS) is then sorted by color to produce one or more single-color sorted polyolefin recycling streams (C) and mixed-color sorted polyolefin recycling streams (CM), wherein each single-color sorted polyolefin recycling stream (C) and the mixed-color sorted polyolefin recycling stream (CM) contains the same polyolefin, the mechanical recycling method for polyolefins according to any one of claims 1 to 7.

19. A mechanical recycling apparatus for polyolefins to carry out the mechanical recycling method for polyolefins according to any one of claims 1 to 7.

Images